Thankfully the passenger seated behind you spoke up to defend you. I'm sure this is the only reason the FA relented, as they realised that should it go further, there was a (presumably) independent witness and the FA would not have a leg to stand on.
I would now be inclined to pursue the FA for threatening you.
That is my exact point. If not for the passenger stepping in, I would have spent the night in Austin or found a circuitous route home as I was on the last direct flight. If it was limited to verbal abuse, I would have let it pass. I did not even respond to his shouting (which took immense self control, I assure you). I have seen enough FAs get upset with passengers for less. I do not think anything I did or said warranted being threatened with removal. That is the only reason I am even pursuing this with United. I do not wish to end the FAs career. I am sure he was just having a bad day. I did not cause it. It gave him no right to act the way he did and call the Captain. Quite frankly I felt sorry for the Captain. I am sure he does not take deplaning a passenger lightly.
No passenger deserves such treatment on any airline.